Laminate and process for its production

ABSTRACT

To provide a laminate excellent in weather resistance, moisture-proof property, adhesion between layers and its long-term stability, and a process for its production. A laminate comprising a substrate sheet containing a fluororesin, an adhesive layer, and a moisture-proof layer containing, as the main component, at least one inorganic compound selected from the group consisting of an inorganic oxide, an inorganic nitride and an inorganic oxynitride, laminated in this order, wherein the adhesive layer contains, as the main component, at least one metal oxide selected from the group consisting of zirconium oxide, tantalum oxide and hafnium oxide.

This application is a continuation of Ser. No. 13/559,746 (filed Jul,27, 2012 and issued on May 7, 2013 as U.S. Pat. No. 8,435,633) which isa continuation of PCT/JP2011/054808 (filed Mar. 2, 2011) and whichclaims priority to JP 2010-056224 (filed Mar. 12, 2010).

TECHNICAL FIELD

The present invention relates to a laminate useful as a protective sheetfor a solar cell module, and a process for its production.

BACKGROUND ART

In recent years, from the viewpoint of the protection of the globalenvironment, clean energy with higher safety, has been desired. Amongclean energies which are expected in the future, particularly a solarcell is highly expected in terms of its cleanness, safety and easyoperation.

The core to convert the sunlight put in a solar cell to electric energyis a cell. As the cell, one composed of a monocrystal, polycrystal oramorphous silicon type semiconductor is widely used. A plurality of thecells are usually wired in series or parallel, and further, they areprotected with various materials for maintaining the function for a longperiod of time, and used as a solar cell module.

A solar cell module generally has a structure where the side of the cellhit by sunlight is covered with a tempered glass, the rear side issealed with a back sheet, and a filer made of a thermoplastic resin(particularly an ethylene/vinyl acetate polymer (hereinafter referred toas “EVA”)) is filled in the space between the cell and the temperedglass and in the space between the cell and the back sheet,respectively.

Quality assurance of product for about 20 to 30 years is required for asolar cell module. Since the solar cell module is mainly used outside,weather resistance is required for the constituent material. Further,the tempered glass and back sheet have a role to prevent thedeterioration caused by the moisture inside the module, andmoisture-proof property is also required.

Although the tempered glass is excellent in not only moisture-proofproperty but also transparency and weather resistance, its plasticity,shock resistance, operability and so on are low. Therefore, theapplication of a resin sheet, particularly a fluororesin sheet excellentin weather resistance, has been considered, instead of the temperedglass. However, the resin sheet has a problem that moisture-proofproperty is low as compared with the tempered glass.

To solve the above-mentioned problem, it has been proposed to provide avapor deposition thin film of an inorganic oxide as a moisture-prooflayer, on a resin sheet. For example, Patent Document 1 proposes aprotective sheet having a fluororesin sheet and a resin sheet having avapor deposition thin film of an inorganic oxide, laminated. Further,Patent Document 2 proposes a protective sheet having a vapor depositionthin film of an inorganic oxide provided on one side of a fluororesinsheet provided, and further having a stain resistant layer and/or anultraviolet absorber layer provided, in order to improve weatherresistance.

However, since the moisture-proof layer has poor adhesion to the resinsheet, when a solar cell module is constituted by providing a fillerlayer so as to be in contacted with the moisture-proof layer, a problemthat the moisture-proof layer peels from the resin sheet, may occur.When a space is created between the resin sheet and the filler layer bythe peeling, the durability of the solar cell module decreases by theimmersion of moisture and the like.

To solve the above-mentioned problem, it has been proposed to provide alayer for improving the adhesion (an adhesive layer) between the resinsheet and the vapor deposition thin film of an inorganic oxide. Forexample, Patent Document 3 proposes to provide an anchor coat layercontaining a complex mixture of an acrylic polyol and/or a polyesterpolyol and an isocyanate compound, between a fluororesin substrate layerand a vapor deposition thin film layer of an inorganic oxide. Further,Patent Document 4 proposes to provide a primer layer for vapordeposition, made of a resin having an amide ester moiety, which isobtained by reacting a resin containing oxazoline groups with an acrylicresin made of a poly(meth)acrylic acid and/or a copolymer of apoly(meth)acrylic acid and a comonomer, in a specific ratio, between asubstrate and a vapor deposition layer made of an inorganic oxide.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: JP-A-2000-138387

Patent Document 2: JP-A-2000-208795

Patent Document 3: JP-A-2009-158778

Patent Document 4: JP-A-2010-16286

DISCLOSURE OF INVENTION Technical Problem

However, even if the adhesive layer is provided, there is a problem thatthe long-term stability of the adhesion between the fluororesin sheetand the moisture-proof film is low.

Under these circumstances, it is an object of the present invention toprovide a laminate excellent in weather resistance, moisture-proofproperty, adhesion between layers and its long-term stability, and aprocess for its production.

Solution to Problem

To solve the above problem, the present invention provides thefollowing.

[1] A laminate comprising a substrate sheet containing a fluororesin, anadhesive layer, and a moisture-proof layer containing, as the maincomponent, at least one inorganic compound selected from the groupconsisting of an inorganic oxide, an inorganic nitride and an inorganicoxynitride, laminated in this order,

wherein the adhesive layer contains, as the main component, at least onemetal oxide selected from the group consisting of zirconium oxide,tantalum oxide and hafnium oxide.

[2] The laminate according to the above [1], wherein the fluororesin isan ethylene/tetrafluoroethylene copolymer.

[3] The laminate according to the above [1] or [2], wherein themoisture-proof layer contains a Si compound or an Al compound as theinorganic compound.

[4] The laminate according to any one of the above [1] to [3], whereinthe moisture-proof layer contains aluminum oxide.

[5] The laminate according to any one of the above [1] to [4], which hasa visible light transmittance of at least 80%.

[6] A protective sheet for a solar cell module, using the laminate asdefined in any one of the above [1] to [5].

[7] A process for producing the laminate as defined in any one of theabove [1] to [5], which comprises:

a step of forming the adhesive layer on at least one side of thesubstrate sheet containing a fluororesin by a dry method, and

a step of forming the moisture-proof layer on the adhesive layer by adry method.

[8] The process according to the above [7], wherein the dry method usedfor forming the adhesive layer or the moisture-proof layer is asputtering method or a plasma chemical vapor deposition method.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a laminateexcellent in weather resistance, moisture-proof property, adhesionbetween layers and its long-term stability, and a process for itsproduction.

DESCRIPTION OF EMBODIMENTS

The laminate of the present invention comprises a substrate sheetcontaining a fluororesin, an adhesive layer, and a moisture-proof layercontaining, as the main component, at least one inorganic compoundselected from the group consisting of an inorganic oxide, an inorganicnitride and an inorganic oxynitride, laminated in this order.

Now, the present invention will be described in further detail.

<Substrate Sheet>

The fluororesin constituting the substrate sheet is not particularlylimited so long as it is a thermoplastic resin containing fluorine atomsin the molecular structure of the resin, and various known fluororesinscan be used. Specifically, a tetrafluoroethylene resin, achlorotrifluoroethylene resin, a vinylidene fluoride resin, a vinylfluoride resin or a composite of at least 2 of these resins may, forexample, be mentioned. Among them, the tetrafluoroethylene resin or thechlorotrifluoroethylene resin is preferred, and the tetrafluoroethyleneresin is particularly preferred, from the viewpoint of the excellence inparticularly weather resistance, stain resistance and the like.

The tetrafluoroethylene resin may, for example, be specificallypolytetrafluoroethylene (PTFE), atetrafluoroethylene/perfluoro(alkoxyethylene) copolymer (PFA), atetrafluoroethylene/hexafluoropropylene/perfluoro(alkoxyethylene)copolymer (EPE), a tetrafluoroethylene/hexafluoropropylene copolymer(FEP), a tetrafluoroethylene/ethylene copolymer (ETFE) or anethylene/trichlorofluoroethylene copolymer (ETCFE).

As a case requires, these resins may further have a small amount of acomonomer component copolymerized respectively.

The comonomer component may be any monomer so long as it iscopolymerizable with other monomers constructing each resin (forexample, in the case of ETFE, tetrafluoroethylene and ethylene). Forexample, the following compounds may be mentioned.

A fluorinated ethylene such as CF₂═CFCl or CF₂═CH₂; a fluorinatedpropylene such as CF₂═CFCF₃ or CF₂═CHCF₃; a C₂₋₁₀ fluorinatedalkylethylene having a fluoroalkyl group such as CH₂═CHC₂F₅, CH₂═CHC₄F₉,CH₂═CFC₄F₉ or CH₂═CF(CF₂)₃H; a perfluoro(alkyl vinyl ether) such asCF₂═CFO(CF₂CFXO)_(m)R^(f) (wherein R^(f) is a C₁₋₆ perfluoroalkyl group,X is a fluorine atom or a trifluoromethyl group, and m is an integer offrom 1 to 5); or a vinyl ether having a group capable of being convertedto a carboxylic acid group or a sulfonic acid group, such asCF₂═CFOCF₂CF₂CF₂COOCH₃ or CF₂═CFOCF₂CF(CF₃OCF₂CF₂SO₂F, may be mentioned.

As the tetrafluoroethylene resin, among them, PFA, FEP, ETFE or ETCFE ispreferred, and particularly, ETFE is preferred from the viewpoint ofcost, mechanical strength, sputtering film forming property and thelike.

ETFE is a copolymer mainly composed of ethylene units andtetrafluoroethylene units. Here, “unit” means a repeating unitconstituting a polymer.

In all the units constituting ETFE, the total content of the ethyleneunits and the tetrafluoroethylene units is preferably at least 90 mol %,more preferably at least 95 mol %, and may be 100 mol %.

In ETFE, the molar ratio of the ethylene units/the tetrafluoroethyleneunits is preferably from 40/60 to 70/30, more preferably from 40/60 to60/40.

As a case requires, ETFE may contain a small amount of comonomercomponent units. As the comonomer component in the comonomer componentunits, the same one as mentioned above may be mentioned.

In a case where ETFE contains comonomer component units, the content ofthe comonomer component units in all the units constituting ETFE ispreferably from 0.3 to 10 mol %, more preferably from 0.3 to 5 mol %.

As the chlorotrifluoroethylene resin, for example, one obtained bysubstituting tetrafluoroethylene of the tetrafluoroethylene resin withchlorotrifluoroethylene may be mentioned. Specifically, achlorotrifluoroethylene homopolymer (CTFE) or anethylene/chlorotrifluoroethylene copolymer (ECTFE) may, for example, bementioned.

The fluororesin contained in a substrate sheet may be one type or two ormore types.

The substrate sheet may be one made of only a fluororesin, or one madeof a mixed resin of a fluororesin and other thermoplastic resin.However, considering the effect of the present invention, it ispreferred that the substrate sheet contains a fluororesin as the maincomponent. The proportion of the fluororesin in the substrate sheet ispreferably at least 50 mass %, more preferably at least 70 mass %, basedon the total mass of the substrate sheet.

Such other thermoplastic resin may, for example, be an acrylic resin, apolyester resin, a polyurethane resin, a nylon resin, a polyethyleneresin, a polyimide resin, a polyamide resin, a polyvinyl chloride resinor a polycarbonate resin.

Further, it is possible to apply a resin obtained by mixing e.g. anadditive and filler such as pigment, ultraviolet absorber, carbon black,carbon fiber, silicon carbide, glass fiber or mica.

The substrate sheet may be subject to surface treatment on the sidewhere the adhesive layer is to be formed, for the improvement of theadhesion between the substrate sheet and the adhesive layer. Surfacetreatment is not particularly limited within a range not to impair theeffects of the present invention, and it is possible to optionallyselect among known surface treatment methods. Specifically, plasmatreatment or corona discharge treatment may, for example, be mentioned.Among them, plasma treatment is preferred, since it is possible to carryout treatment homogenously on the whole of the surface to be treated ofthe substrate sheet, the load on the surface of the substrate sheet issmall and the influence over the for long-term stability of the adhesionis small, or the like.

The shape and size of the substrate sheet may be optionally decidedaccording to the purpose, and are not particularly limited. For example,in a case where the laminate is used for a protective sheet for a solarcell module, they may be optionally decided according to the shape andsize of the solar cell module.

The thickness of the substrate sheet is preferably at least 10 μm, morepreferably at least 20 μm from the viewpoint of the strength. The upperlimit of the thickness may be decided optionally according to thepurpose, and is not limited. For example, in a case where the laminateis used for a protective sheet which is provided on the side of the cellof a solar cell module, where sunlight hits, the thickness is preferablythinner from the viewpoint of the improvement of power generationefficiency by high light transmittance. Specifically, it is preferablyat most 200 μm, more preferably at most 60 μm.

<Adhesive Layer>

The adhesive layer contains, as the main component, at least one metaloxide selected from the group consisting of zirconium oxide, tantalumoxide and hafnium oxide. Here, “containing, as the main component” meansthat the proportion of the metal oxide in the adhesive layer is at least95 mol %. The proportion of the metal oxide in the adhesive layer ispreferably 100 mol %. That is, the adhesive layer is preferably composedof the metal oxide. The adhesive layer is formed on the substrate sheet,whereby it is possible to maintain the adhesion between themoisture-proof layer, to be formed on the adhesive layer and thesubstrate sheet, for a long period of time. Further, since the adhesivelayer is also excellent in transparency, the transparency as the wholeof the laminate is good.

The adhesive layer is preferably formed by a dry method. The film formedby the dry method (vapor deposition film) has an uniform film thicknessas compared with a film formed by a wet method, and has high adhesion tothe substrate sheet.

As the dry method, a physical vapor deposition method (PVD method), achemical vapor deposition method (CVD method) or the like may bementioned.

As the PVD method, a vacuum vapor deposition method, a sputtering methodor an ion plating method may, for example, be mentioned, and any of themmay be used. Among them, particularly the sputtering method ispreferred, since as well as it is excellent in productivity and isindustrially widely used, it is possible to obtain a film with a uniformthickness, which is very dense and has a high adhesion to the substratesheet. As the sputtering method, any of a direct-current sputteringmethod, a high-frequency sputtering method and an alternating-currentsputtering method can be used. The direct-current sputtering method orthe alternating-current sputtering method is preferred, since it isexcellent in productivity e.g. it is possible to efficiently form a filmwith a high film forming rate on a substrate having a large area.

As the CVD method, a plasma CVD method, a thermal CVD method or acatalyst CVD method may, for example, be mentioned, and any of them canbe used. Among them, the plasma CVD method is preferred, since as wellas it is excellent in productivity and is industrially widely used, itis possible to obtain a film with a uniform thickness, which is verydense and has a high adhesion to the substrate sheet.

The specific forming conditions of the adhesive layer can be determinedoptionally according to the methods and materials to be used.

For example, a zirconium oxide film is obtained by forming by asputtering method in an oxygen-containing atmosphere by using azirconium target. In this case, by a method of applying intermittentnegative direct-current voltage to the target, it is possible tosuppress the arcing during film forming effectively, increase inputpower, and maintain a further high film forming rate for a long periodof time. The specific sputtering conditions may be selected optionally,since the conditions vary depending on various conditions such as anapparatus type and the target composition. Generally, it is preferred tocarry out the sputtering under the conditions where after evacuation tofrom 1×10⁻⁴ Pa to 8×10⁻⁴ Pa, argon and oxygen are introduced into areactor in a flow rate of 0:100 to 90:10, with a sputtering gas pressureof from 0.2 to 3 Pa at a power density of from 0.5 to 5 W/cm².

A tantalum oxide film or a hafnium oxide film can be formed in the samemanner as in the above step except that a tantalum target or a hafniumtarget is used instead of a zirconium target.

The adhesive layer may be one made of a single layer or one made ofmultiple layers differing in the type of the metal oxide.

The film thickness of the adhesive layer (when it is made of multiplelayers, the thickness is the total thickness) is preferably at least 0.5nm with a view to securing adhesion to the substrate sheet. Further, itis preferably at most 20 nm, particularly preferably at most 10 nm, witha view to maintaining light transmittance, maintaining flexibility ofthe substrate sheet and securing adhesion to the substrate sheet.

<Moisture-Proof Layer>

The moisture-proof layer contains, as the main component, at least oneinorganic compound selected from the group consisting of an inorganicoxide, an inorganic nitride and an inorganic oxynitride.

Here, “containing, as the main component” means that the proportion ofthe inorganic compound in the moisture-proof layer is at least 95 mol %.The proportion of the inorganic compound in the moisture-proof layer ispreferably 100 mol %. That is, the moisture-proof layer is preferablyone composed of the inorganic compound, or one containing the inorganiccompound.

The inorganic oxide may, for example, be a meal oxide. As the metal inthe metal oxide, aluminum, silicon or magnesium may, for example, bementioned. As the oxide, particularly silicon oxide (SiO_(x), 0<x≦2) oraluminum oxide (AlO_(x), 0<x≦1.5) is preferred.

As the inorganic nitride, silicon nitride (SiN_(x), 0<x≦1.3) or aluminumnitride (AlN_(x), 0<x≦1) may, for example, be mentioned.

As the inorganic oxynitride, silicon oxynitride (SiO_(x)N_(y), 0<x<1,0<y<1) may, for example, be mentioned.

As the inorganic compound, a Si compound or an Al compound is preferred,since it is excellent in transparency, water vapor barrier property andthe like. Particularly, as the Si compound, preferred is at least onemember selected from the group consisting of SiO_(x) (0<x≦2), SiN_(x)(0<x≦1.3) and SiO_(x)N_(y) (0<x<1, 0<y<1), and as the Al compound,AlO_(x) (0<x≦1.5) is preferred.

The moisture-proof layer may be formed by a dry method or a wet method,however, the dry method is preferred. The film formed by the dry method(vapor deposition film) has a uniform thickness as compared with a filmformed by the wet method, and has high adhesion to the adhesive layer.

As the dry method, a physical vapor deposition method (PVD method), achemical vapor deposition method (CVD method) or the like may bementioned.

As the PVD method, a vacuum vapor deposition method, a sputtering methodor an ion plating method may, for example, be mentioned, and any of themmay be used. Among them, particularly the sputtering method ispreferred, since as well as it is excellent in productivity and isindustrially widely used, it is possible to obtain a film with a uniformthickness, which is very dense and has a high adhesion to the adhesivelayer. As the sputtering method, any of a direct-current sputteringmethod, a high-frequency sputtering method and an alternating-currentsputtering method can be used. The direct-current sputtering method orthe alternating-current sputtering method is preferred, since it isexcellent in productivity, e.g. it is possible to efficiently form afilm with a high film forming rate on a substrate having a large area.

As the CVD method, a plasma CVD method, a thermal CVD method or acatalyst CVD method may, for example, be mentioned, and any of them canbe used. Among them, the plasma CVD method is preferred, since as wellas it is excellent in productivity and is industrially widely used, itis possible to obtain a film with a uniform thickness, which is verydense and has a high adhesion to the substrate sheet.

The specific forming condition of the moisture-proof layer can bedetermined optionally according to the methods and materials to be used.

For example, an aluminum oxide film is obtained by forming by asputtering method in an oxygen-containing atmosphere by using analuminum target. In this case, by a method of applying intermittentnegative direct-current voltage to the target, it is possible tosuppress the arcing during film forming effectively, increase inputpower, and maintain a further high film forming rate for a long periodof time. The specific sputtering conditions may be selected optionally,since the conditions vary depending on various conditions such as anapparatus type target composition. Generally, it is preferred to carryout the sputtering under the conditions where after evacuation to from1×10⁻⁴ Pa to 8×10⁻⁴ Pa, argon and oxygen are introduced into a reactorin a flow rate of 0:100 to 90:10, with a sputtering gas pressure of from0.2 to 3 Pa and with a power density of from 0.5 to 5 W/cm².

The moisture-proof layer may be one made of a single layer or one madeof multiple layers differing in the material (for example, an inorganiccompound as the main component).

The film thickness of the moisture-proof layer (when it is made ofmultiple layers, the thickness is the total thickness) is preferably atleast 10 nm from the viewpoint of moisture-proof property. Further, itis preferably at most 50 nm, particularly preferably at most 30 nm, witha view to maintaining light transmittance, maintaining flexibility ofthe substrate sheet and securing adhesion to the substrate sheet.

The laminate of the present invention has the above constitution,whereby it is excellent in weather resistance, moisture-proof property,adhesion between layers and its long-term stability. That is, since theadhesive layer contains a specific metal oxide as the main component,the adhesion between the adhesive layer and the moisture-proof layer,and between the adhesive layer and the substrate sheet, is high.Therefore, the adhesion and its long-term stability as the wholelaminate are high. Further, since the adhesive layer has hightransparency, the whole laminate is also excellent in transparency.

Therefore, the laminate of the present invention is useful as aprotective sheet for a solar cell module.

For example, since the adhesion and its long-term stability as the wholelaminate are high, according to the solar cell module wherein thelaminate is provided so that the moisture-proof layer side is on theside of the filler layer of e.g. EVA, reduction in the adhesive strengthbetween the substrate sheet and the filler layer hardly occurs.

Further, with respect to the laminate, since the substrate sheet, theadhesive layer and the moisture-proof layer have high transparencyrespectively, transparency is high as the whole laminate. Therefore, thelaminate can be used as a protective sheet for protecting the side wheresunlight hits in the solar cell module.

Here, in a case where the laminate of the present invention is used as aprotective sheet for protecting the side where sunlight hits in thesolar cell module, the visible light transmittance of the laminate ispreferably at least 80%, more preferably at least 85%, furtherpreferably at least 90%. The upper limit is not particularly limitedsince the higher the visible light transmittance is, the better it is.However, it is practically about 98%.

Further, the substrate sheet containing a fluororesin is excellent inweather resistance, heat resistance, chemical resistance and furtherstain resistance. Therefore, when the laminate is provided so that theoutermost layer of the solar cell module is the substrate sheet, it ispossible to prevent the performance from decreasing by stains for a longperiod of time, since dust or trash is unlikely to be attached to thesurface of the solar cell module.

EXAMPLES

Now, the present invention will be described in further detail withreference to Examples. However, the present invention is by no meansrestricted thereto.

Here, measuring methods and evaluation methods used in the followingExamples are as follows.

[Measurement of Visible Light Transmittance]

Spectral transmission spectrum was measured by using a spectrometer(tradename “UV-3100PC” manufactured by Shimadzu Corporation) and thevisible light transmittance (%) was calculated from the measured valuebased on JIS R3106-1998.

[Film Thickness of Each Layer]

Film thickness was measured by using a spectral ellipsometry device(tradename “M-2000DI” manufactured by J.A. WOOLLAM JAPAN), andcalculated by carrying out optical fitting by “WVASE32” (manufactured byJ.A. WOOLLAM).

[Evaluation of Adhesion]

One having the laminate obtained in each of Examples and ComparativeExamples cut to a size of 10 cm×10 cm and an EVA film cut to the samesize (“W25CL” manufactured by Bridgestone Corporation) were laminated inthe order of ETFE film/adhesive layer/moisture-proof layer/EVA film(only in Comparative Example 1, the order of ETFE film/moisture-prooflayer/EVA film), followed by thermocompression bonding under conditionsof pressure of 10 kgf/cm by a press machine (manufactured by Asahi GlassCompany, Limited), area of 120 cm², temperature of 150° C. and time of10 minutes to obtain a test specimen.

Then, each test specimen was cut to a size of 1 cm×10 cm, and using aTENSILON universal testing machine “RTC-1310A” manufactured by OrientecCo., Ltd., adhesive strength (peeling adhesive strength, unit: N/cm) wasmeasured by 180° peeling test in accordance with JIS K6854-2, at apulling rate of 50 mm/min.

The measurement of the adhesive strength was carried out before (initialstage) and after the following weathering test. However, weathering testwas not carried out for one having the initial adhesive strength of lessthan 1 N/cm.

Weathering test: carried out for 100 hours by using a sunshine carbonarc lamp weathering test machine (Sunshine weather meter S 300manufactured by Suga Test Instruments Co., Ltd.), in accordance withJIS-B7753.

One having adhesive strength of at least 5 N/cm after weathering test ismarked with ◯, and one at most that value is marked with ×. Further, onehaving the initial adhesive strength of less than 1 N/cm is also markedwith ×.

Example 1

An ETFE film having a thickness of 100 μm (tradename “Aflex”,manufactured by Asahi Glass Company, Limited) was provided inside asputter devise (manufactured by Tokki) to adjust vacuum to about 8×10⁻⁴Pa, and 40 sccm of Ar gas and 10 sccm of O₂ gas were introduced into achamber to adjust the pressure to be 0.3 Pa. Then, plasma was generatedby applying direct-current voltage with power of 200 W. Zirconium wasused as a target and a shatter was opened and closed to control formingtime to form 5 nm of a zirconium oxide thin film on the ETFE film. Then,aluminum was used as a target and 50 sccm of Ar gas and 3 sccm of O₂ gaswere introduced into a chamber, followed by discharge at 320 V ofdirect-current voltage. The shatter was opened and closed to controlforming time, whereby 20 nm of an aluminum oxide thin film was formedand a laminate comprising ETFE film/zirconium oxide (adhesivelayer)/aluminum oxide (moisture-proof layer) was prepared.

With respect to the laminate, the measurement of a visible lighttransmittance (%) and the evaluation for adhesion were carried out. Theresults are shown in Table 1.

Example 2

A laminate comprising ETFE film/tantalum oxide (adhesive layer)/aluminumoxide (moisture-proof layer) was prepared in the same manner as in theabove Example 1 except that tantalum was used as a target instead ofaluminum to form 5 nm of a tantalum oxide thin film.

With respect to the laminate, the measurement of a visible lighttransmittance (%) and the evaluation of adhesion were carried out. Theresults are shown in Table 1.

Example 3

A laminate comprising ETFE film/hafnium oxide (adhesive layer)/aluminumoxide (moisture-proof layer) was prepared in the same manner as in theabove Example 1 except that hafnium was used as a target instead ofaluminum to form 5 nm of a hafnium oxide thin film.

With respect to the laminate, the measurement of a visible lighttransmittance (%) and the evaluation of adhesion were carried out. Theresults are shown in Table 1.

Comparative Example 1

An ETFE film having a thickness of 100 μm (tradename “Aflex”,manufactured by Asahi Glass Company, Limited) was provided inside asputter devise (manufactured by Tokki) to adjust vacuum to about 8×10⁻⁴Pa, and 50 sccm of Ar gas and 3 sccm of O₂ gas were introduced into achamber, followed by discharge at 320 V of direct-current voltage. Ashatter was opened and closed to control forming time, whereby 20 nm ofan aluminum oxide thin film was formed and a laminate comprising ETFEfilm/aluminum oxide (moisture-proof layer) was prepared.

With respect to the laminate, the measurement of a visible lighttransmittance (%) and the evaluation of adhesion were carried out. Theresults are shown in Table 1.

Since the laminate of Comparative Example 1 had a weak initial adhesivestrength of 0.1 N/cm, weathering test was not conducted.

Further, after the measurement of the initial adhesive strength, thepeeling interface was evaluated by a fluorescent X ray, and it was foundthat the ETFE film and the aluminum oxide thin film were peeled at theirinterface.

Comparative Example 2

A laminate comprising ETFE film/SUS oxide (adhesive layer)/aluminumoxide (moisture-proof layer) was prepared in the same manner as in theabove Example 1 except that a stainless steel (SUS 304) was used insteadof aluminum to form 5 nm of a SUS oxide thin film.

With respect to the laminate, the measurement of a visible lighttransmittance (%) and the evaluation of adhesion were carried out. Theresults are shown in Table 1.

Comparative Example 3

In the same manner as in the above Example 1 except that a tin-aluminumalloy (Sn:Al=50 mass %:50 mass %, hereinafter referred to as Sn-50Al)was used instead of aluminum to form 5 nm of a Sn-50Al oxide thin film,a laminate comprising ETFE film/Sn-50Al oxide (adhesive layer)/aluminumoxide (moisture-proof layer) was prepared.

With respect to the laminate, the measurement of a visible lighttransmittance (%) and the evaluation of adhesion were carried out. Theresults are shown in Table 1.

Comparative Example 4

In the same manner as in the above Example 1 except that a tin-chromiumalloy (Sn:Cr=70 mass %:30 mass %, hereinafter referred to as Sn-30Cr)was used instead of aluminum to form 5 nm of a Sn-30Cr oxide thin film,a laminate comprising ETFE film/Sn-30Cr oxide (adhesive layer)/aluminumoxide (moisture-proof layer) was prepared.

With respect to the laminate, the measurement of a visible lighttransmittance (%) and the evaluation of adhesion were carried out. Theresults are shown in Table 1.

Comparative Example 5

A laminate comprising ETFE film/chromium oxide (adhesive layer)/aluminumoxide (moisture-proof layer) was prepared in the same manner as in theabove Example 1 except that chromium was used instead of aluminum toform 5 nm of a chromium oxide thin film.

With respect to the laminate, the measurement of a visible lighttransmittance (%) and the evaluation of adhesion were carried out. Theresults are shown in Table 1.

Comparative Example 6

A laminate comprising ETFE film/niobium oxide (adhesive layer)/aluminumoxide (moisture-proof layer) was prepared in the same manner as in theabove Example 1 except that niobium was used instead of aluminum to form5 nm of a niobium oxide thin film.

With respect to the laminate, the measurement of a visible lighttransmittance (%) and the evaluation of adhesion were carried out. Theresults are shown in Table 1.

Since the laminate of Comparative Example 6 had a weak initial adhesivestrength of 0.9 N/cm, weathering test was not conducted.

Comparative Example 7

A laminate comprising ETFE film/molybdenum oxide (adhesivelayer)/aluminum oxide (moisture-proof layer) was prepared in the samemanner as in the above Example 1 except that molybdenum was used insteadof aluminum to form 5 nm of a molybdenum oxide thin film.

With respect to the laminate, the measurement of a visible lighttransmittance (%) and the evaluation of adhesion were carried out. Theresults are shown in Table 1.

Since the laminate of Comparative Example 7 had a weak initial adhesivestrength of 0.1 N/cm, weathering test was not conducted.

Comparative Example 8

In the same manner as in the above Example 1 except that atungsten-titanium alloy (W:Ti=90 mass %:10 mass %, hereinafter referredto as W-10Ti) was used instead of aluminum to form 5 nm of a W-10Tioxide thin film, a laminate comprising ETFE film/W-10Ti oxide (adhesivelayer)/aluminum oxide (moisture-proof layer) was prepared.

With respect to the laminate, the measurement of a visible lighttransmittance (%) and the evaluation of adhesion were carried out. Theresults are shown in Table 1.

Example 4

An ETFE film having a thickness of 100 μm (tradename “Aflex”,manufactured by Asahi Glass Company, Limited) was provided inside asputter devise (manufactured by Tokki) to adjust vacuum to about 8×10⁻⁴Pa, 50 scm of Ar gas was introduced and the pressure inside the sputterdevise was controlled to 2.6 Pa by a variable valve. Plasma wasgenerated by applying 60 W of RF (radio frequency) to the substrate tocarry out surface treatment for 60 seconds. Then, 40 sccm of Ar gas and10 sccm of O₂ gas were introduced into a chamber to adjust the pressureto be 0.3 Pa. Then, plasma was generated by applying direct-currentvoltage with power of 200 W. Zirconium was used as a target and ashatter was opened and closed to control forming time to form 5 nm of azirconium oxide thin film on the ETFE film. Then, aluminum was used as atarget and 50 sccm of Ar gas and 3 sccm of O₂ gas were introduced into achamber, followed by discharge at 320 V of direct-current voltage. Theshatter was opened and closed to control forming time, whereby 20 nm ofan aluminum oxide thin film was formed and a laminate comprising ETFEfilm/zirconium oxide (adhesive layer)/aluminum oxide (moisture-prooflayer) was prepared.

With respect to the laminate, a visible light transmittance (%) and theadhesion strength (initial and after weathering test) were measured. Theresults are shown in Table 1.

Example 5

A laminate comprising ETFE film/tantalum oxide (adhesive layer)/aluminumoxide (moisture-proof layer) was prepared in the same manner as in theabove Example 1 except that tantalum was used as a target instead ofaluminum to form 5 nm of a tantalum oxide thin film.

With respect to the laminate, the measurement of a visible lighttransmittance (%) and the evaluation of adhesion were carried out. Theresults are shown in Table 1.

Example 6

A laminate comprising ETFE film/hafnium oxide (adhesive layer)/aluminumoxide (moisture-proof layer) was prepared in the same manner as in theabove Example 1 except that hafnium was used as a target instead ofaluminum to form 5 nm of a hafnium oxide thin film.

With respect to the laminate, the measurement of a visible lighttransmittance (%) and the evaluation of adhesion were carried out. Theresults are shown in Table 1.

TABLE 1 Adhesion Adhesive strength (N/cm) After weathering test for 100Constitution Tv (%) Initial hours Evaluation Ex. 1 ETFE/ZrO₂/Al₂O₃ 93.925.0 8.4 ◯ Ex. 2 ETFE/Ta₂O₅/Al₂O₃ 91.9 28.9 18.5 ◯ Ex. 3 ETFE/HfO/Al₂O₃94.5 25.0 22.0 ◯ Comp. Ex. 1 ETFE/Al₂O₃ 92.3 0.1 — X Comp. Ex. 2ETFE/SUS-oxide/Al₂O₃ 81.2 23.1 1.0 X Comp. Ex. 3 ETFE/Sn—50Aloxide/Al₂O₃ 90.1 22.7 1.0 X Comp. Ex. 4 ETFE/Sn—30Cr oxide/Al₂O₃ 84.48.4 1.0 X Comp. Ex. 5 ETFE/CrO/Al₂O₃ 80.3 1.6 0.3 X Comp. Ex. 6ETFE/Nb₂O₅/Al₂O₃ 88.6 0.9 — X Comp. Ex. 7 ETFE/MoO/Al₂O₃ 84.0 0.1 — XComp. Ex. 8 ETFE/W—10Ti oxide/Al₂O₃ 86.3 8.8 0.6 X Ex. 4 ETFE/ZrO₂/Al₂O₃93.9 25.2 7.4 ◯ Ex. 5 ETFE/Ta₂O₅/Al₂O₃ 91.9 27.4 15.3 ◯ Ex. 6ETFE/HfO/Al₂O₃ 94.5 27.4 20.2 ◯

As shown in the above results, as compared with the laminate inComparative Example 1, on which an adhesive layer was not provided, thelaminates in Examples 1 to 3 had the same or higher visible lighttransmittance (Tv) and high transparency. Further, the initial adhesivestrength was improved largely, and a certain degree of adhesive strengthwas maintained even after weathering test. With respect to the laminatesin Examples 4 to 6, which had the same constitution as the ones inExamples 1 to 3 respectively except that surface treatment was carriedout for a ETFE film, almost similar results were obtained.

On the other hand, as compared with the laminate in Comparative Example1, on which an adhesive layer was not provided, the laminates inComparative Examples 2 to 8 had a low visible light transmittance (Tv)and decreased transparency. Further, the evaluation result for adhesionwas poor, and for example, in Comparative Examples 2 and 3, the initialadhesive strength was relatively good, however, the adhesive strengthafter weathering test decreased largely. In Comparative Examples 4, 5and 8, the initial adhesive strength was low as compared with Examples 1to 6, and further, the adhesive strength after weathering test decreaseddrastically. In Comparative Examples 6 and 7, the initial adhesivestrength was less than 1.0 N/cm.

Industrial Applicability

The laminate of the present invention is excellent in weatherresistance, moisture-proof property, adhesion between layers and itslong-term stability, and is useful for a protective sheet for a solarcell module.

This application is a continuation of PCT Application No.PCT/JP2011/054808, filed on Mar. 2, 2011, which is based upon and claimsthe benefit of priority from Japanese Patent Application No. 2010-056224filed on Mar. 12, 2010. The contents of those applications areincorporated herein by reference in its entirety.

What is claimed is:
 1. A laminate comprising a substrate sheet containing an ethylene/tetrafluoroethylene copolymer, an adhesive layer, and a moisture-proof layer containing at least 95 mol % of at least one inorganic compound selected from the group consisting of an inorganic oxide, an inorganic nitride and an inorganic oxynitride, laminated in this order, wherein the adhesive layer contains at least 95 mol % of at least one metal oxide selected from the group consisting of zirconium oxide, tantalum oxide and hafnium oxide, and wherein the thickness of the moisture-proof layer is at most 50 nm.
 2. The laminate according to claim 1, wherein the moisture-proof layer contains a Si compound or an Al compound as the inorganic compound.
 3. The laminate according to claim 1, wherein the moisture-proof layer contains aluminum oxide.
 4. The laminate according to claim 1, which has a visible light transmittance of at least 80%.
 5. A protective sheet for a solar cell module, comprising the laminate of claim
 1. 6. The laminate according to claim 1, wherein the thickness of the moisture-proof layer is at most 30 nm.
 7. The laminate according to claim 1, wherein the thickness of the adhesive layer is 0.5 to 20 nm.
 8. The laminate according to claim 1, wherein the thickness of the substrate sheet is 10 to 200 μm. 